A technique to culture rabbit uterine epithelial cells in chemically defined medium has been developed. Estrogens were found to increase cell proliferation, while progesterone antagonized this effect. The primary cultures were found to be made up of quiescent or nondividing and dividing cells which show interactions. The cultures were also found to produce the rabbit uterus secretory protein uteroglobin. We will continue to study our experimental system by a) Isolating and characterizing factors regulating the estrogen-proliferative effect as well as determining their mechanism of action, b) Studying the role of plastic vs. collagen as substrates for growth in modulating proliferation, differentiation and hormonal responses, c) Studying the regulation of uteroglobin production in relation to different growth substrates, cell cycle and hormone additions using RIA, and molecular or "in situ" cDNA/RNA hybridization, d) Determining the mechanisms regulating estrogen and progesterone receptors in cells grown in different substrates or quiescent vs. dividing cells or regulated by hormones, and e) similar studies will be attempted in cloned cell lines, which will provide tools for further studies using cell fusion and to a certain extent somatic cell genetic. The endpoint of our research is to improve our comprehension of the mechanisms by which sex hormones regulate proliferation and differentiation of endometrium. It is expected that the study of our hormone-responsive systems will help to advance the understanding of the etiology and pathogenesis of endometrial carcinoma as well as of several critical problems in reproductive biology.